Wireless Power System With Battery Charge Indicators

ABSTRACT

A wireless power system includes a wireless power transmitting device such as a wireless charging mat for charging devices such as a cellular telephone and an earbuds battery case. The earbuds battery case receives earbuds and charges the earbuds from a battery. The wireless charging mat supports bidirectional in-band communications between the cellular telephone and the earbuds battery case. The earbuds battery case provides the cellular telephone with information on the battery charge level associated with the battery in the earbuds battery case and a battery charge level associated with each earbud in the earbuds battery case. The cellular telephone receives battery charge level information through the wireless charging mat and displays corresponding indicators. The earbuds battery case has a visual output device such as a light-emitting diode that is illuminated to indicate that the earbuds battery case is being charged.

This application is a divisional of patent application Ser. No.16/026,931, filed Jul. 3, 2018, which claims the benefit of provisionalpatent application No. 62/556,236, filed on Sep. 8, 2017, which arehereby incorporated by reference herein in their entireties.

FIELD

This relates generally to power systems, and, more particularly, towireless power systems for charging electronic devices.

BACKGROUND

In a wireless charging system, a wireless charging mat wirelesslytransmits power to a portable electronic device that is placed on themat. The portable electronic device has wireless power receivingcircuitry that receives the wirelessly transmitted power.

In some arrangements, it can be difficult to determine whether equipmentin a wireless power system is operating satisfactorily. For example, itmay be difficult to determine which devices in a system are receivingpower, it may be difficult to ascertain battery charge levels, and itmay be difficult to determine which portable devices are associated witheach other.

SUMMARY

A wireless power system includes a wireless power transmitting devicesuch as a wireless charging mat. The wireless charging mat has coilsthat transit wireless power signals to one or more wireless powerreceiving devices. The wireless power receiving devices can include acellular telephone and a battery case for an accessory such as anearbuds battery case.

An earbuds battery case receives earbuds and uses a wired connection tocharge the earbuds from a battery within the earbuds battery case. Thewireless charging mat is used in forming bidirectional in-bandcommunications links with the cellular telephone and the earbuds batterycase.

The earbuds battery case provides the cellular telephone withinformation on the battery charge level associated with the battery inthe earbuds battery case and a battery charge level associated with eachearbud in the earbuds battery case. The cellular telephone receives thischarge level information wirelessly through the wireless charging matand displays battery charge level indicators on a display in thecellular telephone.

The earbuds battery case has a visual output device such as alight-emitting diode that is illuminated to indicate that the earbudsbattery case is being charged. The illumination of the light-emittingdiode may be synchronized with the presentation of the battery chargelevel information on the display of the cellular telephone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative wireless chargingsystem that includes a wireless power transmitting device and wirelesspower receiving devices in accordance with an embodiment.

FIG. 2 is a side view of an illustrative wireless charging mat anddevices on the mat that are receiving wireless power in accordance withan embodiment.

FIG. 3 is a top view of an illustrative wireless charging mat on whichan accessory such as a pair of earbuds and an associated earbud batterycase have been placed and on which a device such as a cellular telephonehas been placed in accordance with an embodiment.

FIG. 4 is a flow chart of illustrative operations involved in operatinga wireless power system in accordance with an embodiment.

DETAILED DESCRIPTION

A wireless power system has a wireless power transmitting device such asa wireless charging mat. The wireless power transmitting devicewirelessly transmits power to one or more wireless power receivingdevices such as wristwatches, media players, cellular telephones, tabletcomputers, laptop computers, accessories such as audio accessories(e.g., headphones, earbuds, etc.), computer mice, trackpads, stylusdevices, or other electronic equipment. In some configurations, thewireless power receiving devices include battery cases (sometimesreferred to as battery packs, supplemental batteries, covers, etc.). Asan example, a wireless power transmitting device may be used inwirelessly charging battery cases for earbuds.

Wireless power receiving devices use power from a wireless powertransmitting device for powering circuitry in the wireless powerreceiving devices and for charging an internal battery. A wireless powerreceiving device such as a battery case for a pair of earbuds transfersbattery power from the battery case to a pair of earbuds that have beenreceived within an interior portion of the battery case using a wiredconnection.

The wireless power transmitting device has one or more wireless powertransmitting coils arranged under a charging surface. During operation,the wireless power transmitting coils are used to transmit wirelesspower signals that are received by a wireless power receiving coil inthe wireless power receiving device. Wireless power signals aretransmitted at a wireless power transmission frequency such as afrequency of about 128 kHz, frequencies in a range between 100 kHz and200 kHz, or other suitable frequency.

An illustrative wireless power system (wireless charging system) isshown in FIG. 1. As shown in FIG. 1, wireless power system 8 includes awireless power transmitting device such as wireless power transmittingdevice 12 and includes wireless power receiving devices 24. Wirelesspower transmitting device 12 includes control circuitry 16. Eachwireless power receiving device 24 includes control circuitry 30.Control circuitry in system 8 such as control circuitry 16 and controlcircuitry 30 is used in controlling the operation of system 8. Thiscontrol circuitry includes processing circuitry associated withmicroprocessors, power management units, baseband processors, digitalsignal processors, microcontrollers, and/or application-specificintegrated circuits with processing circuits. The processing circuitryimplements desired control and communications features in devices 12 and24. For example, the processing circuitry may be used in determiningpower transmission levels, processing sensor data, processing userinput, handling communications between devices 12 and 24 (e.g., sendingand receiving in-band and out-of-band data), displaying information ondevice 12 and/or device(s) 24, selecting wireless power transmittingcoils, and otherwise controlling the operation of system 8. If desired,control circuitry in system 8 may be used to authorize components to usepower and ensure that components do not exceed maximum allowable powerconsumption levels.

Control circuitry in system 8 may be configured to perform operations insystem 8 using hardware (e.g., dedicated hardware or circuitry),firmware and/or software. Software code for performing operations insystem 8 is stored on non-transitory computer readable storage media(e.g., tangible computer readable storage media) in control circuitry 8.The software code may sometimes be referred to as software, data,program instructions, instructions, or code. The non-transitory computerreadable storage media may include non-volatile memory such asnon-volatile random-access memory (NVRAM), one or more hard drives(e.g., magnetic drives or solid state drives), one or more removableflash drives or other removable media, or the like. Software stored onthe non-transitory computer readable storage media may be executed onthe processing circuitry of control circuitry 16 and/or 30. Theprocessing circuitry may include application-specific integratedcircuits with processing circuitry, one or more microprocessors, acentral processing unit (CPU), digital signal processing circuits,baseband processors, power management units with processing circuitry,microcontrollers, and other processing circuitry.

Power transmitting device 12 may be a stand-alone power adapter (e.g., awireless charging mat that includes power adapter circuitry), may be awireless charging mat that receives power from a power adapter or otherequipment using a cable, may be a portable device, may be equipment thathas been incorporated into furniture, a vehicle, or other system, or maybe other wireless power transfer equipment. Illustrative configurationsin which wireless power transmitting device 12 is a wireless chargingmat are sometimes described herein as an example.

Each power receiving device 24 may be a portable electronic device suchas a wristwatch, a cellular telephone, a laptop computer, a tabletcomputer, an earbuds battery case or other accessory battery case, audioequipment such as earbuds or headphones (e.g., earbuds that wirelesslycommunicate with a cellular telephone, tablet computer, or otherelectronic device using a wireless connection such as a Bluetooth®link), other accessories, or other electronic equipment. Powertransmitting device 12 may receive power from a wall outlet (e.g.,alternating current), may have a battery for supplying power, and/or mayhave another source of power.

Power transmitting device 12 of FIG. 1 has an AC-DC power converter suchas power converter 14 for converting AC power from a wall outlet orother power source into DC power. DC power is used to power controlcircuitry 16. During operation, a controller in control circuitry 16uses power transmitting circuitry 52 to transmit wireless power to powerreceiving circuitry 54 of each device 24. Power transmitting circuitry52 has switching circuitry (e.g., inverter circuitry 60 formed fromtransistors) that is turned on and off at an alternating-currentwireless power transmission frequency based on control signals providedby control circuitry 16. This creates AC current signals through one ormore coils 42. Coils 42 may be arranged in a planar coil array (e.g., inconfigurations in which device 12 is a wireless charging mat). Coils 42can overlap with adjacent coils 42.

As AC currents pass through one or more coils 42, alternating-currentelectromagnetic fields (signals 44) are produced that are received byone or more corresponding coils such as coil 48 in each power receivingdevice 24. When the alternating-current electromagnetic fields arereceived by coil 48, corresponding alternating-current currents areinduced in coil 48. Rectifier circuitry such as rectifier 50, whichcontains rectifying components such as synchronous rectificationmetal-oxide-semiconductor transistors arranged in a bridge network,converts received AC signals (received alternating-current signalsassociated with electromagnetic signals 44) from coil 48 into DC voltagesignals for powering device 24.

The DC voltages produced by rectifier 50 can be used in powering abattery such as battery 58 and can be used in powering other componentsin each device 24. For example, device 24 may include input-outputdevices 56 such as a display (e.g., a touch screen display) or othervisual output device (e.g., a light-emitting diode or other visualindicator device), a touch sensor (separate from the display or part ofa display), communications circuits, audio components, sensors, andother components and these components may be powered by the DC voltagesproduced by rectifier 50 (and/or DC voltages produced by battery 58).

Device 12 and/or device(s) 24 may communicate wirelessly using in-bandor out-of-band communications. Device 12 may, for example, have wirelesstransceiver circuitry 40 (e.g., wireless local area network circuits,Bluetooth® circuits, cellular telephone transceiver circuitry, etc.)that wirelessly transmits out-of-band signals to device 24 using anantenna. Wireless transceiver circuitry 40 may be used to wirelesslyreceive out-of-band signals from device 24 using the antenna. Eachdevice 24 may have transmitter circuitry in wireless transceivercircuitry 46 that transmits out-of-band signals to device 12. Receivercircuitry in wireless transceiver 46 may use an antenna to receiveout-of-band signals from device 12.

Wireless transceiver circuitry 40 uses one or more coils 42 to transmitin-band signals to wireless transceiver circuitry 46 that are receivedby wireless transceiver circuitry 46 using coil 48. Any suitablemodulation scheme may be used to support in-band communications betweendevice 12 and device 24. In some configurations, frequency-shift keying(FSK) is used to convey in-band data from device 12 to device 24 andamplitude-shift keying (ASK) is used to convey in-band data from device24 to device 12. Power is conveyed wirelessly from device 12 to device24 during these FSK and ASK transmissions.

During wireless power transmission operations, circuitry 52 supplies ACdrive signals to one or more coils 42 at a given power transmissionfrequency. The power transmission frequency may be, for example, apredetermined frequency of about 128 kHz, at least 80 kHz, at least 100kHz, less than 500 kHz, less than 300 kHz, less than 200 kHz, 100-200kHz, 50-200 kHz, 100-200 kHz, or other suitable wireless powerfrequency. In some configurations, device 12 varies the powertransmission frequency during operation.

In configurations that support FSK in-band communications, wirelesstransceiver circuitry 40 uses FSK modulation to modulate the powertransmission frequency of the driving AC signals that device 12 is usingto transmit wireless power and thereby modulates the frequency ofsignals 44. In each device 24, coil 48 is used to receive signals 44.Power receiving circuitry 54 uses the received signals on coil 48 andrectifier 50 to produce DC power. At the same time, wireless transceivercircuitry 46 uses FSK demodulation to extract the transmitted in-banddata from signals 44. This approach allows FSK data (e.g., FSK datapackets) to be transmitted in-band from device 12 to device 24 withcoils 42 and 48 while power is simultaneously being wirelessly conveyedfrom device 12 to device 24 using coils 42 and 48.

In configurations that support ASK in-band communications wirelesstransceiver circuitry 46 transmits in-band data to device 12 by using aswitch (e.g., one or more transistors in transceiver 46 that areconnected to coil 48) to modulate the impedance of power receivingcircuitry 54 (e.g., coil 48). This, in turn, modulates the amplitude ofsignal 44 and the amplitude of the AC signal passing through coil(s) 42.Wireless transceiver circuitry 40 monitors the amplitude of the ACsignal passing through coil(s) 42 and, using ASK demodulation, extractsthe transmitted in-band data from these signals that was transmitted bywireless transceiver circuitry 46. The use of ASK communications allowsASK data bits (e.g., ASK data packets) to be transmitted in-band fromdevice 24 to device 12 with coils 48 and 42 while power issimultaneously being wirelessly conveyed from device 12 to device 24using coils 42 and 48.

Control circuitry 16 has external object measurement circuitry 41(sometimes referred to as foreign object detection circuitry or externalobject detection circuitry) that detects external objects on a chargingsurface associated with device 12. Circuitry 41 can detect foreignobjects such as coils, paper clips, and other metallic objects and candetect the presence of wireless power receiving devices 24. Controlcircuitry 30 has measurement circuitry 43. Measurement circuitry 41 and43 may be used in making inductance measurements (e.g., measurements ofthe inductances of coils 42 and 48), input and output voltagemeasurements (e.g., a rectifier output voltage, and inverter inputvoltage, etc.), current measurements, capacitance measurements,frequency measurements (e.g., measurements of the frequency of wirelesspower signals), and/or other measurements on the circuitry of system 8.

FIG. 2 is a diagram of system 8 in an illustrative configuration inwhich wireless power transmitting device 12 is a wireless charging mat,a first wireless power receiving device that receives power fromwireless charging mat 12 is a cellular telephone or other portabledevice with a display (see, e.g., cellular telephone 24A, which may havea touchscreen) and a second wireless power receiving device thatreceives power from wireless charging mat 12 is an earbuds case with abattery (see, e.g., earbuds battery case 24B, which may not have atouchscreen). The third device in the illustrative configuration of FIG.2 is a pair of earbuds 24C (e.g., earbuds 24C that receive audiowirelessly from cellular telephone 24A). Earbuds 24C are received withininterior region 71 of earbuds battery case housing 73 (e.g., a housingformed from plastic, metal, fabric, leather, and/or other materials.Earbuds 24C include left earbud 24C1, which is configured to be receivedwithin the left ear of a user, and right earbud 24C2, which isconfigured to be received within the right ear of a user. Earbuds 24Ccontain batteries (battery 58 of FIG. 1) and may receive battery powerfrom the batteries in earbud case 24B via wired connections. Forexample, each earbud has a connector 70 that mates with a correspondingconnector 72 in earbuds case 24B so that earbuds case 24B may transferpower from a battery in earbuds case 24B to earbuds 24C and so thatearbuds 24C can communicate over the wired connection (e.g., the contactconnections formed from contacts in connectors 70 and 72) with controlcircuitry in case 24B. If desired, earbuds 24C may each include powerreceiving circuitry 54 for wirelessly receiving power directly from awireless power transmitting device such as wireless charging mat 12.Wireless power transfer operations (inductive charging) and wirelessdata communications in system 8 between devices 24 and/or device 12 arecontactless (e.g., not wired).

FIG. 3 shows how cellular telephone 24A has a display such as display74. During operation, cellular telephone 24A uses display 74 and/orother input-output devices to display information for a user on thebattery charge level (sometimes referred to as battery charge status,battery state of charge, battery charge information, etc.) for some orall of the devices on mat 12. As shown in FIG. 3, for example, thecontrol circuitry of cellular telephone 24A uses display 74 to displaycellular telephone battery charge level information 76 (e.g., a batterycharge level indicator) indicative of the state of charge of the batteryin cellular telephone 24A, uses display 74 to display earbuds casebattery charge level information 78, and/or uses display 74 to displayearbuds battery charge level information 80 (e.g., separate charge levelinformation for left earbud 24C1 and right earbud 24C2). Thisinformation is conveyed to cellular telephone 24A wirelessly in system8.

With one illustrative configuration, battery charge information fromcase 24B and earbuds 24C can be conveyed wirelessly to cellulartelephone 24A via mat 12 (e.g., using in-band communications).Information associated with battery charging can also be conveyedwirelessly from cellular telephone 24A to case 24B and earbuds 24C viamat 12 (e.g., using in-band communications). Case 24B, which may containearbuds 24C, has input-output devices such as light-emitting diode 82(or other visual output device such as a display, a tone generator, aspeaker, and/or other input-output component). Case 24B useslight-emitting diode 82 to produce visual output (e.g., steady and/orflashing light, etc.) in response to changes in battery charging statusor other criteria. For example, case 24B may illuminate light-emittingdiode 82 when case 24B is receiving wireless power from mat 12 and ischarging its internal battery.

Illustrative operations associated with operating system 8 are shown inthe flow chart of FIG. 4. During the operations of block 90, a userperforms a pairing process to pair cellular telephone and earbuds 24C(e.g., by opening case 24B in the vicinity of cellular telephone 24A andclicking on an on-screen option that is presented on cellular telephone24A to form a connection between earbuds 24C and cellular telephone24A). Earbuds 24C, case 24B, and/or cellular telephone 24A may, ifdesired, communicate wirelessly to support pairing operations (e.g., toexchange and compare device identifiers, etc.). In an illustrativeconfiguration, earbuds 24C are coupled to case 24B using a wiredconnection (see, e.g., connectors 70 and 72 of FIG. 2) and this wiredconnection is used by case 24B to obtain the identifier associated witheach earbud 24C. During the pairing operations of block 90, wirelessearbuds 24C are paired with (associated with) cellular telephone 24A andare paired with case 24B. Case 24B may retain information on theidentity of paired earbuds in case 24B and information on the identifierof the most recent earbuds received within case 24B. This allows case24B to compare the identifier for earbuds that are currently enclosed incase 24 to a previously paired earbud identifier.

Earbuds case 24B may take action based on compared identifiers. Forexample, in response to determining that case 24B contains earbuds 24Cthat do not match a previously paired set of earbuds, case 24B may flashlight-emitting diode 82 to warn the user that the user may haveinadvertently put earbuds that belong to someone else into case 24B.Because case 24B gathers earbud identifiers that identify the earbuds24C in case 24B, case 24B is sometimes said to inherit the identify ofearbuds 24C.

Following pairing operations, a user may place cellular telephone 24Aand earbuds case 24B (and any earbuds 24C in case 24B) on mat 12 forwireless charging. During the operations of block 92 and block 94,cellular telephone 24A may send an identifier (e.g., a cellulartelephone identifier) to mat 12 and case 24B may obtain an identifier(e.g., an earbuds identifier) that is associated with the earbuds 24C incase 24B and send that earbuds identifier to mat 12. Wireless chargingmat 12 supplies wireless power to the devices on mat 12 when obtainingthe identifiers (e.g., to ensure that the devices are provided withadequate power to operate their communications circuitry and to allowin-band communications to be used to transmit the identifierinformation).

In an illustrative configuration, mat 12 initially senses that a reevingdevice is present (e.g., using a foreign object detection process thatsenses foreign objects based on measured coil inductances and/or otherinformation gathered with measurement circuitry 41). This initialsensing reveals whether a given receiving device is a small low-powerdevice such as an earbuds case or watch or is a high-power device suchas a cellular telephone. Mat 12 can then provide initial wireless powerbased on the anticipated power rating of the receiving device. Once thereceiving device identifier has been received by mat 12, mat 12 canadjust the amount of wireless power that is transmitted to a level thatis appropriate for the type of receiving device that is present. Thereceiving device can thereafter supply real time power level adjustmentrequests to mat 12 (e.g., via in-band communications) that serve todirect mat 12 to increase or decrease transmitted power levelsaccordingly.

After the identifier information of blocks 92 and 94 has been receivedby mat 12, mat 12 may, during the operations of block 96, establishbidirectional communications between mat 12 and cellular telephone 24Aand between mat 12 and case 24B. The bidirectional communications linksthat are established in this way allow cellular telephone 24A and case24B to communicate wirelessly (e.g., using in-band communications). Mat12 serves as an intermediary and relays messages between cellulartelephone 24A and case 24B. Case 24B can communicate with earbuds 24A incase 24B using a wired connection (see, e.g., the connection formed byconnectors 70 and 72 in FIG. 2). Using the bidirectional in-band linkformed through mat 12, battery charge level information and otherinformation can be exchanged during operation of system 8.

The amount of wireless power that is being delivered to case 24B can bereduced when it is desired to operate case 24B in a battery maintenancemode in which the charge state of case 24B is being maintained at afully charged level or other desired level and in which the circuitry ofcase 24B is powered and able to handle wireless communications. Thisallows earbuds 24C to wirelessly transmit battery status information tocellular telephone 24A via mat 12. Firmware updates may also besupported (e.g., cellular telephone 24A may receive firmware updateswirelessly that are transmitted to case 24B via mat 12 so that case 24Bmay provide these firmware updates to earbuds 24C). When earbuds 24C arein a wirelessly powered case, wireless communications circuitry inearbuds 24C (e.g., Bluetooth® circuitry) may be maintained in an activestate to support cellular telephone pairing operations. In scenarios inwhich earbuds 24C are in a case that is not being wirelessly powered,the earbuds may be placed in a quiescent state (e.g., a low-power sleepstate) to conserve battery life. In scenarios in which case 24B on mat12 is empty, wireless power transfer to case 24B can be periodicallyhalted to conserve power and periodically reestablished to ensure thatthe battery in case 24B remains fully charged.

During the operations of block 98, system 8 may be used in displayingbattery information for a user. For example, cellular telephone 24A maydisplay battery charge level information (sometimes referred to as stateof charge information) using charge level icons 76, 78, and 80 of FIG. 3and battery case 24B may illuminate light-emitting diode 82 to indicateto the user that mat 12 is currently charging case 24B. The state ofcharge of the battery in each earbud 24C may be conveyed to case 24Bover a wired connection (e.g., connectors 70 and 72 of FIG. 2). Thestate of charge of case 24B and the state of charge of earbuds 24C incase 24B may be provided to cellular telephone 24A from case 24B usingin-band communications (e.g., the bidirectional communications linkbetween case 24B and cellular telephone 24A that was established duringthe operations of block 96). Control circuitry 16 in cellular telephone24A gathers information on the state of charge of its batteryinternally.

The display of battery charging information on display 74 of cellulartelephone 24A and the illumination of light-emitting diode 82 may becoordinated, so that the battery charging information appears on display74 in synchronization with the illumination of diode 82 (e.g., thevisual output associated with these two items may commence at anidentical time or nearly identical time such as times that are within200 ms of each other, within 100 ms of each other, etc.). To ensure thatlight-emitting diode 82 is illuminated at the same time that display 74first presents information 76, 78, and 80 to the user, cellulartelephone 24A may, during the operations of block 98, transmit acase-specific countdown timer value to case 24B. The countdown timervalue is specific to case 24 B (to accommodate multiple cases on mat 12)and informs that case 24B of the amount of time that will elapse beforedisplay 74 is used in displaying information 76, 78, and 80. Case 24Breceives the countdown timer value and starts a corresponding countdowntimer. When the countdown timer expires (e.g., at the same moment thatdisplay 74 is first being used to display information 76, 78, and 80such as shortly after cellular telephone 24A is placed on mat 12), case24B illuminates light-emitting diode 82 or other visual status indicatorin case 24B.

The behavior of system 8 in displaying battery charge information for auser may vary depending on whether a user's earbuds 24C or the earbudsof another person are present in case 24B, whether case 24B belongs tothe user or to another person, whether case 24B is empty, and otherfactors.

For example, consider a first scenario, in which a user's cellulartelephone 24A is placed on mat 12 and the case 24B of another personthat contains the earbuds 24C of that other person are placed on mat 12.In this scenario, neither the case nor the earbuds on the mat are ownedby the user and are therefore not paired with the cellular telephone 24Aof the user. As a result, cellular telephone 24A will only displaybattery status information 76. In some configurations, light-emittingdiode 82 may be illuminated while case 24B is wirelessly charged, butthe illumination of light-emitting diode 82 will not be coordinated withthe display of information 76 on display 74 using a countdown timervalue, because cellular telephone 24A does not recognize the case anddoes not recognize the earbuds. The same result would be obtained if theearbuds of the other person were to be placed in the case 24B of theuser (because case 24B inherits the identity of the earbuds 24C receivedwithin case 24B).

In a second scenario, a user places the user's earbuds 24C in a borrowedcase 24B belonging to another person and places case 24B and the user'scellular telephone 24A on mat 12. The earbuds 24C were previously pairedwith the user's cellular telephone. In this scenario, the borrowed case24B inherits the identifier of the earbuds 24C that are contained withinthe borrowed case. Cellular telephone 24A was previously paired withearbuds 24C and therefore displays information 76, 78, and 80 on display74. In anticipation of displaying this information on display 74,cellular telephone 24A transmits an appropriate countdown timer value tocase 24B. This allows case 24B and cellular telephone 24A tosimultaneously activate and thereby synchronously display information76, 78, and 80 (on display 74) and illuminate light-emitting diode 82(on case 24B).

In a third scenario, a users' empty case 24B is placed on mat 12 with auser's cellular telephone 24A. If the case previously contained theuser's earbuds 24C, this information is retained by case 24B, solight-emitting diode 82 may be illuminated at the same time thatcellular telephone 24A displays charge status information 76 and 78.Charge status information 80 is not displayed, because earbuds 24C arenot present. If the case previously contained the earbuds 24C of anotherperson (e.g., earbuds 24C are not paired with cellular telephone 24A),case battery status information 78 is omitted from display 74 andlight-emitting diode 82 is not synchronized with the battery statusinformation displayed on display 74. The same result is obtained if case24B belongs to another person, because this aspect of the behavior ofsystem 8 depends on the identity of the last earbuds 24B present in case24B.

In a fourth scenario, a user's case 24B containing the user's earbuds24C is placed on mat 12 and the user's cellular telephone 24A is placedon mat 12. As described in connection with the operations of block 98,cellular telephone 24A will transmit countdown time value to case 24B,so that information 76, 78, and 80 is displayed on display 74simultaneously with the illumination of light-emitting diode 82 on case24B.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. An earbuds battery case operable with earbuds,comprising: a housing; a battery; a connector configured to form aconnection with earbuds received within the housing; and controlcircuitry that is configured to: receive earbud identifiers for earbudsreceived within the housing; and retain at least a given earbudidentifier that is associated with a pair of the earbuds that mostrecently were received within the housing.
 2. The earbuds battery caseof claim 1 wherein the control circuitry is configured to: transmit theretained earbud identifier to a wireless power transmitting device whilethe corresponding earbud is not connected with the connector.
 3. Theearbuds battery case of claim 2 further comprising wireless powerreceiving circuitry configured to receive wireless power from thewireless power transmitting device, wherein the control circuitry isconfigured to transmit the retained earbud identifier using in-bandcommunications.
 4. The earbuds battery case of claim 3 furthercomprising a light-emitting diode, wherein the control circuitry isconfigured to illuminate the light-emitting diode in response toreceiving information from the wireless power transmitting device. 5.The earbuds battery case of claim 1 wherein the control circuitry isconfigured to receive firmware updates from the wireless powertransmitting device using in-band communications.
 6. The earbuds batterycase of claim 5 wherein the control circuitry is configured to transmitthe firmware update to the earbuds.
 7. A system operable with a wirelesspower transmitting device, comprising: a first wireless power receivingdevice configured to receive wireless power from the wireless powertransmitting device; a wired power receiving device configured toreceive power from the first wireless power receiving device and totransmit an identifier to the first wireless power receiving device; anda second wireless power receiving device configured to receive wirelesspower from the wireless power transmitting device and to receive theidentifier from the first wireless power receiving device.
 8. The systemof claim 7, wherein the first wireless power receiving device furthercomprises: a visual output device; control circuitry configured tocompare the identifier to a previously received identifier and todisplay a visual output on the visual output device in response todetermining that the identifier does not match the previously receivedidentifier.
 9. The system of claim 8, wherein the visual output devicecomprises a light-emitting diode.
 10. The system of claim 7, wherein thesecond wireless power receiving device further comprises: a visualoutput device; control circuitry configured to compare the identifier toa previously received identifier and to display a visual output on thevisual output device in response to determining that the identifier doesnot match the previously received identifier.
 11. The system of claim 10wherein the visual output device comprises a display with a touchscreen.12. The system of claim 11, wherein the control circuitry is configuredto use the display to display a battery charge level indicatorcorresponding to a level of battery charge on a battery in the wiredpower receiving device in response to determining that the identifiermatches the previously received identifier.
 13. The system of claim 7,wherein the wired power receiving device comprises wirelesscommunications circuitry configured to transmit wireless signalsdirectly to the second wireless power receiving device.
 14. The systemof claim 13, wherein the wired power receiving device is configured tooperate in a first state while the first wireless power receiving devicereceives wireless power and a second state while the first wirelesspower receiving device is not receiving wireless power and wherein thewireless communications circuitry is configured to transmit the wirelesssignals when the wired power receiving device is in the first state. 15.The system of claim 14 wherein the second state comprises a low-powersleep state.
 16. The system of claim 7, wherein the first wireless powerreceiving device is configured to transmit real time power leveladjustment requests to the wireless power transmitting device.
 17. Anearbuds battery case operable with earbuds, comprising: a housing withan interior configured to receive a first pair of earbuds; powerdelivery circuitry configured to transfer power to the earbuds; andcontrol circuitry that is configured to: receive a first earbudidentifier for the first pair earbuds; and retain at least a givenearbud identifier that is associated with a second pair of earbuds. 18.The earbuds battery case of claim 17 further comprising: wirelesscommunications circuitry configured to wirelessly transmit the firstearbud identifier.
 19. The earbuds battery case of claim 18 wherein thecontrol circuitry is configured to transmit the retained earbudidentifier using in-band communications.
 20. The earbuds battery case ofclaim 17 further comprising: a light-emitting diode, wherein the controlcircuitry is configured to compare the first earbud identifier to thesecond earbud identifier and illuminate the light-emitting diode inresponse to determining that the first earbud identifier does not matchthe second earbud identifier.